In the next year we plan to continue our investigations of the organization and expression of the mitochrondrial genome in HeLa cells. In particular, the mapping on the Hpa II restriction map of mitochondrial DNA of the discrete poly (A)-containing RNA components and individual specific tRNA species which are transcribed from this DNA and of the promoters for transcription will be pursued. The nucleotide sequence of a small fragment containing the origin of replication of HeLa cell mitochondrial DNA will be determined. The coding capacity of mitochondrial DNA-coded poly(A)-containing RNA for defined products of mitochondrial protein synthesis will be investigated in a cell-free system. The synthesis and assembly of the polypeptide components of human cytochrome c oxidase will be analyzed.